267 lines
12 KiB
XML
267 lines
12 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<chapter version="5.0" xml:id="advanced_configuration"
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xmlns:ns3="http://www.w3.org/1998/Math/MathML"
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xmlns:ns="http://docbook.org/ns/docbook">
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<?dbhtml stop-chunking?>
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<title>Advanced Configuration</title>
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<para>OpenStack is intended to work well across a variety of installation
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flavors, from very small private clouds to large public clouds. To achieve
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this, the developers add configuration options to their code that allow the
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behavior of the various components to be tweaked depending on your needs.
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Unfortunately, it is not possible to cover all possible deployments with the
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default configuration values.<indexterm class="singular">
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<primary>advanced configuration</primary>
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<see>configuration options</see>
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</indexterm><indexterm class="singular">
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<primary>configuration options</primary>
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<secondary>wide availability of</secondary>
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</indexterm></para>
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<para>At the time of writing, OpenStack has more than 3,000 configuration
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options. You can see them documented at <link
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xlink:href="http://docs.openstack.org/liberty/config-reference/content/config_overview.html">the OpenStack configuration reference
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guide</link>. This chapter cannot hope to document all of these, but we do
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try to introduce the important concepts so that you know where to go digging
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for more information.</para>
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<section xml:id="driver_differences">
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<title>Differences Between Various Drivers</title>
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<para>Many OpenStack projects implement a driver layer, and each of these
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drivers will implement its own configuration options. For example, in
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OpenStack Compute (nova), there are various hypervisor drivers
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implemented—libvirt, xenserver, hyper-v, and vmware, for example. Not all
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of these hypervisor drivers have the same features, and each has different
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tuning requirements.<indexterm class="singular">
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<primary>hypervisors</primary>
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<secondary>differences between</secondary>
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</indexterm><indexterm class="singular">
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<primary>drivers</primary>
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<secondary>differences between</secondary>
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</indexterm></para>
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<note>
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<para>The currently implemented hypervisors are listed on <link
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xlink:href="http://docs.openstack.org/liberty/config-reference/content/section_compute-hypervisors.html">the OpenStack documentation
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website</link>. You can see a matrix of the various features in
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OpenStack Compute (nova) hypervisor drivers on the OpenStack wiki at
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<link xlink:href="http://docs.openstack.org/developer/nova/support-matrix.html">the Hypervisor support matrix
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page</link>.</para>
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</note>
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<para>The point we are trying to make here is that just because an option
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exists doesn't mean that option is relevant to your driver choices.
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Normally, the documentation notes which drivers the configuration applies
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to.</para>
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</section>
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<section xml:id="periodic_tasks">
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<title>Implementing Periodic Tasks</title>
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<para>Another common concept across various OpenStack projects is that of
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periodic tasks. Periodic tasks are much like cron jobs on traditional Unix
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systems, but they are run inside an OpenStack process. For example, when
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OpenStack Compute (nova) needs to work out what images it can remove from
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its local cache, it runs a periodic task to do this.<indexterm
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class="singular">
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<primary>periodic tasks</primary>
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</indexterm><indexterm class="singular">
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<primary>configuration options</primary>
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<secondary>periodic task implementation</secondary>
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</indexterm></para>
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<para>Periodic tasks are important to understand because of limitations in
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the threading model that OpenStack uses. OpenStack uses cooperative
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threading in Python, which means that if something long and complicated is
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running, it will block other tasks inside that process from running unless
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it voluntarily yields execution to another cooperative thread.<indexterm
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class="singular">
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<primary>cooperative threading</primary>
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</indexterm></para>
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<para>A tangible example of this is the <literal>nova-compute</literal>
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process. In order to manage the image cache with libvirt,
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<literal>nova-compute</literal> has a periodic process that scans the
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contents of the image cache. Part of this scan is calculating a checksum
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for each of the images and making sure that checksum matches what
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<literal>nova-compute</literal> expects it to be. However, images can be
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very large, and these checksums can take a long time to generate. At one
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point, before it was reported as a bug and fixed,
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<literal>nova-compute</literal> would block on this task and stop
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responding to RPC requests. This was visible to users as failure of
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operations such as spawning or deleting instances.</para>
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<para>The take away from this is if you observe an OpenStack process that
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appears to "stop" for a while and then continue to process normally, you
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should check that periodic tasks aren't the problem. One way to do this is
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to disable the periodic tasks by setting their interval to zero.
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Additionally, you can configure how often these periodic tasks run—in some
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cases, it might make sense to run them at a different frequency from the
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default.</para>
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<para>The frequency is defined separately for each periodic task.
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Therefore, to disable every periodic task in OpenStack Compute (nova), you
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would need to set a number of configuration options to zero. The current
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list of configuration options you would need to set to zero are:</para>
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<itemizedlist>
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<listitem>
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<para><literal>bandwidth_poll_interval</literal></para>
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</listitem>
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<listitem>
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<para><literal>sync_power_state_interval</literal></para>
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</listitem>
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<listitem>
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<para><literal>heal_instance_info_cache_interval</literal></para>
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</listitem>
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<listitem>
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<para><literal>host_state_interval</literal></para>
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</listitem>
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<listitem>
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<para><literal>image_cache_manager_interval</literal></para>
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</listitem>
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<listitem>
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<para><literal>reclaim_instance_interval</literal></para>
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</listitem>
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<listitem>
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<para><literal>volume_usage_poll_interval</literal></para>
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</listitem>
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<listitem>
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<para><literal>shelved_poll_interval</literal></para>
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</listitem>
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<listitem>
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<para><literal>shelved_offload_time</literal></para>
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</listitem>
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<listitem>
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<para><literal>instance_delete_interval</literal></para>
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</listitem>
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</itemizedlist>
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<para>To set a configuration option to zero, include a line such as
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<literal>image_cache_manager_interval=0</literal> in your
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<filename>nova.conf</filename> file.</para>
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<para>This list will change between releases, so please refer to your
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configuration guide for up-to-date information.</para>
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</section>
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<section xml:id="specific-advanced-config-topics">
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<title>Specific Configuration Topics</title>
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<para>This section covers specific examples of configuration options you
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might consider tuning. It is by no means an exhaustive list.</para>
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<section xml:id="adv-config-security">
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<title>Security Configuration for Compute, Networking, and
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Storage</title>
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<para>The <emphasis><link xlink:href="http://docs.openstack.org/sec/">OpenStack
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Security Guide</link></emphasis> provides a deep dive into securing an
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OpenStack cloud, including SSL/TLS, key management, PKI and certificate
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management, data transport and privacy concerns, and
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compliance.<indexterm class="singular">
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<primary>security issues</primary>
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<secondary>configuration options</secondary>
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</indexterm><indexterm class="singular">
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<primary>configuration options</primary>
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<secondary>security</secondary>
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</indexterm></para>
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</section>
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<section xml:id="adv-config-ha">
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<title>High Availability</title>
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<para>The <emphasis><link
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xlink:href="http://docs.openstack.org/ha-guide/index.html">OpenStack High Availability
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Guide</link></emphasis> offers suggestions for elimination of a single
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point of failure that could cause system downtime. While it is not a
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completely prescriptive document, it offers methods and techniques for
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avoiding downtime and data loss.<indexterm class="singular">
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<primary>high availability</primary>
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</indexterm><indexterm class="singular">
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<primary>configuration options</primary>
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<secondary>high availability</secondary>
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</indexterm></para>
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</section>
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<section xml:id="adv-config-ipv6">
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<title>Enabling IPv6 Support</title>
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<para>You can follow the progress being made on IPV6 support by
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watching the <link xlink:href="https://wiki.openstack.org/wiki/Meetings/Neutron-IPv6-Subteam">neutron IPv6
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Subteam at work</link>.<indexterm class="singular">
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<primary>Liberty</primary>
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<secondary>IPv6 support</secondary>
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</indexterm><indexterm class="singular">
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<primary>IPv6, enabling support for</primary>
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</indexterm><indexterm class="singular">
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<primary>configuration options</primary>
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<secondary>IPv6 support</secondary>
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</indexterm></para>
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<para>By modifying your configuration setup, you can set up IPv6 when
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using <literal>nova-network</literal> for networking, and a tested setup
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is documented for FlatDHCP and a multi-host configuration. The key is to
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make <literal>nova-network</literal> think a <literal>radvd</literal>
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command ran successfully. The entire configuration is detailed in a
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Cybera blog post, <link xlink:href="http://www.cybera.ca/news-and-events/tech-radar/an-ipv6-enabled-cloud/">“An IPv6
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enabled cloud”</link>.</para>
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</section>
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<section xml:id="adv-config-geography">
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<title>Geographical Considerations for Object Storage</title>
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<para>Support for global clustering of object storage servers
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is available for all supported releases. You would implement these global
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clusters to ensure replication across geographic areas in case of a
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natural disaster and also to ensure that users can write or access their
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objects more quickly based on the closest data center. You configure a
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default region with one zone for each cluster, but be sure your network
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(WAN) can handle the additional request and response load between
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zones as you add more zones and build a ring that handles more zones.
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Refer to <link
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xlink:href="http://docs.openstack.org/developer/swift/admin_guide.html#geographically-distributed-clusters">Geographically Distributed
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Clusters</link> in the documentation for additional
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information.<indexterm class="singular">
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<primary>Object Storage</primary>
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<secondary>geographical considerations</secondary>
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</indexterm><indexterm class="singular">
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<primary>storage</primary>
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<secondary>geographical considerations</secondary>
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</indexterm><indexterm class="singular">
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<primary>configuration options</primary>
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<secondary>geographical storage considerations</secondary>
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</indexterm></para>
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</section>
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</section>
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</chapter>
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